than the diameter of piles. Spacing is decided based on type of soil and level of design moments but it should not be too large, otherwise pieces of lumps etc. drop and extra precautions are needed. Cohesive soils or soils having some cohesion are suitable. No water table should be present. Acceptable amount of water is collected at the base and pumped out. Common diameters are 0.60, 0.80, 1.00 m. Waling beams (usually called ?breasting beams ) are Tangent piles with grouting in between are used when secant piling or diaphragm walling equipment is not available (i.e. in cases where ground water exists). Poor workmanship creates significant problems.
Secant bored pile walls are formed by keeping spacing of piles less than diameter (S There is also need for place for the plant. It may be constructed “hard-hard”as well as “soft-hard”. “S oft”concrete pile contains low cement content and some bentonite. Primary unreinforced piles are constructed first and then reinforced secondary piles are formed by cutting the primary piles. Pile construction methods may vary in different countries for all type of pile walls like full casing support, bentonite support, continuous flight auger (CFA) etc. mostly reinforced concrete but sheet pile sections or steel beams are also used. Diaphr agm Walls Diaphragm wall provides structural support and water tightness. It is a classical technique for many deep excavation projects, large civil engineering works, underground car parks, metro pits etc. especially under water table. These reinforced concrete diaphragm (continuous) walls are also called slurry trench walls due to the reference given to the construction technique where excavation of wall is made possible by filling and keeping the wall cavity full with bentonite-water mixture during excavation to prevent collapse of the excavated vertical surfaces. Wall thickness varies between 0.50 m and 1.50 m. The wall is constructed panel by panel in full depth.Panel lengths are 2 m to 10 m. Short lengths (2-2.5 m) are selected in unstable soils or under very high surcharges. Nowadays depth of panels water stops exceeded 100 m, excavation depths exceeded 50 m. Different panel shapes other than the conventional straight section like T, L, H, Y, + are possible to form and used for special purposes. Panel excavation is made by cable or kelly supported buckets and by a recent design called ?cutter or ?hydrofraise which is a pair of hydraulically operated rotating disks provided with hard cutting tools. Excavation in rock is possible. Slurry wall technique is a specialized technique and apart from the bucket or the frame carrying the cutter equipment like crawler crane, pumps, tanks, desanding equipment, air lifts, screens, cyclones, silos, mixers, extractor are needed. Tremie concrete is placed in the slurry starting from the bottom after lowering reinforcement cages. Joint between the panels is a significant detail in water bearing soils and steel pipe, H-beam or water stops are used. R einforced C oncrete R eta ining Walls Excavation in Stages It is a common type of staged excavation wall usually supported by ground anchors. Soils with some cohesion are suitable because each stage is first excavated before formwork and concrete placement. No water table or appreciable amount of water should be present. Sometimes micropile support is given if required due to expected cave-ins. Soil Nail Walls Similar to the method above excavation is made step by step (1.5 to 2 m high). Shotcrete is common for facing and wiremesh is used. Soft facing is also possible making use of geotextiles. Hole is drilled, ordinary steel bars are lowered, and grout is placed without any pressure. Soil should be somewhat cohesive and no water table or significant water flow should be present. Coffer dams Cofferdam is a temporary earth retaining structure to be able to make excavation for construction activities. It is usually preferred in the coastal and sea environment like bridge piers and abutments in rivers, lakes etc., wharves, quay walls, docks, break waters and other structures for shore protection, large waterfront structures such as pump houses, subjected to heavy vertical and horizontal loads. Sheet piling is commonly used in various forms other than conventional walls like circular cellular bodies or double walls connected inside and filled with sand. Stability is maintained by sheeting driven deeper than base, sand body between sheeting and inside tie rods. Earth embankments and concrete bodies are also used. Contiguous, tangent, secant piles or diaphragm walls are constructed in circular shapes, and no internal bracing or anchoring is used to form a cofferdam. Reinforced concrete waling beams support by arching. Shafts are also made with this method. Large excavations or project details may require additional lateral support. J et Grout and Deep M ixed Walls Retaining walls are made by single to triple row of jet grout columns or deep mixed columns. There is a soil mixed wall(SMW) technique specially developed for wall construction where H sections are used for reinforcement. Single reinforcing bar is placed in the central hole opened for jet grout columns. Anchors, nails or struts may be used for support. Top Down Constr uction Retaining structure (generally diaphragm wall) is designed and constructed as permanent load bearing walls of basement. Piles or barettes are similarly placed to complete the structural frame. Top slab is cast at the ground surface level, and excavation is made under the slab by smaller sized excavators and continued down forming basement slabs at each level. There are special connection details. Top down method is preferred in highly populated city centers where horizontal and vertical displacements are very critical, and anchors and struts are very difficult to use due to complex underground facilities and lifeline structures and site operations are difficult to perform. Pa r tia l Excavation or Island M ethod It is possible to give strut support to retaining walls at a later stage after constructing central sections of a building in large size excavations. Core of the structure is built at the central part making sloped excavations at peripheral areas and then the core frame is used to give support to walls (Figure 1.9). It may be more practical and construction time may be less compared to conventional braced system. This method may not be suitable in soft and weak soils due to stability and deformation problems during sloped excavations. 2. EARTH PR ESSUR ES ON IN-SITU R ETAINING WAL L S Introduction Earth pressures on in-situ retaining walls are rather different than those on ordinary retaining walls due to the supporting elements. Free displacement of walls are not allowed. Type of support affects the distribution of earth pressure. Strut loads were measured in strutted excavations in many countries in the past, and recommendations were given. Ground anchor technology is relatively new, and data on instrumented anchored walls for total lateral 百度搜索“70edu”或“70教育网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，70教育网，提供经典综合文库地下室设计深基坑中英文对照外文翻译文献(2)在线全文阅读。
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